Embossed polypropylene band has been widely used for packing goods and various synthetic resin-made tightening devices for such band are disclosed in the U.S. Pat. No. 3,206,816 and 3,414,943, but none are found to be satisfactory. When the band is thick, the legs of the tightening device are liable to be distorted due to a lack of mechanical strength; and even when the band is thin, the tightening device permits the band to get loose if a shock is applied to a folded portion of the tightened band, or near the tightening device.